The overall concept of the project is that TGF? receptor regeneration mediates the repression of survivin thereby contributing to the anti tumor activity associated with histone deacetylase inhibitors (HDACi). It is thought that HDACi efficacy would be improved by less promiscuity with respect to the range of HDAC's inhibited by currently available agents. Thus, identification of a key HDAC(s) controlling TGF? receptor repression would be of consequence for the development of appropriate strategies. Our preliminary data point to HDAC1 as a mediator of TGF? receptor repression in cancer. Transcriptional repression of TGF? receptor expression and hence its tumor suppressor gene (TSG) activity occurs frequently in colon and breast cancer cells. This is consistent with the frequent loss of these receptors at both the protein and mRNA levels in patient samples by mechanisms that are unlikely to be associated with mutations of TGF? signaling components. Loss of receptor expression is associated with poor prognosis in these patients as well (3). Loss of TGF? receptors as well as signaling was reversed by treatment with HDACi inhibitors. In other work we have found that a novel endogenous cell death pathway targeting repression of survivin expression is an important element of TGF? TSG activity. Consequently, we will test the hypothesis that tumor inhibition associated with inhibition of HDAC activity is linked to TGF? TSG activity through this novel autocrine death pathway in Specific Aim I. Stable expression of HDAC1 SiRNA regenerated deficient TGF? receptor expression thus implying that HDAC1 is responsible for transcriptional repression of the receptors. During this cycle of the project we found that reactivation of the TGF? receptor transcription was dependent upon the HDAC inhibition at several Sp1 sites. However, these sites differed with respect to transcription factor usage. Consequently, the hypothesis that different mechanisms of response to HDAC inhibition occurs at different Sp1 sites in the RII promoter will be tested in Aim II. The hypotheses that HDACi and specific HDAC1 inhibition activates an intrinsic survivin mediated death pathway in xenograft models will be tested in Specific Aim III. Characterization of this new stable HDAC1 knockdown model could lead to the identification of rational combination approaches based on complementary mechanisms of action. The Specific Aims are: 1) DETERMINE WHETHER HDAC 1 INHIBITION is SUFFICIENT FOR REGENERATION OF BOTH TGF? RECEPTORS AND REPRESSION OF P21 AND SURVIVIN. 2) DETERMINATION OF THE MECHANISMS OF ACTIVATION &SILENCING OF TGF? TRANSCRIPTION 3) DETERMINE WHETHER HDAC 1 KNOCKDOWN IS SUFFICIENT TO OBTAIN ANTI-TUMOR ACTIVITY IN XENOGRAFTS.